Field of the Invention
The present invention relates to a resist composition containing a base component which generates acid upon exposure and also exhibits changed solubility in a developing solution under the action of acid, and a method of forming a resist pattern using the resist composition.
Priority is claimed on Japanese Patent Application No. 2011-068798, filed Mar. 25, 2011, the content of which is incorporated herein by reference.
Description of Related Art
In lithography techniques, for example, a resist film composed of a resist material is formed on a substrate, and the resist film is subjected to selective exposure, followed by development, thereby forming a resist pattern having a predetermined shape on the resist film. A resist material in which the exposed portions of the resist film become soluble in a developing solution is called a positive-type, and a resist material in which the exposed portions of the resist film become insoluble in a developing solution is called a negative-type.
In recent years, in the production of semiconductor elements and liquid crystal display elements, advances in lithography techniques have led to rapid progress in the field of pattern miniaturization.
Typically, these miniaturization techniques involve shortening the wavelength (increasing the energy) of the exposure light source. Conventionally, ultraviolet radiation typified by g-line and i-line radiation has been used, but nowadays KrF excimer lasers and ArF excimer lasers are starting to be introduced in mass production. Furthermore, research is also being conducted into lithography techniques that use an exposure light source having a wavelength shorter (energy higher) than these excimer lasers, such as extreme ultraviolet radiation (EUV), electron beam (EB) and X ray.
Resist materials for use with these types of exposure light sources require lithography properties such as a high resolution capable of reproducing patterns of minute dimensions, and a high level of sensitivity to these types of exposure light sources.
As a resist material which satisfies these conditions, a chemically amplified resist composition has been used conventionally, which includes an acid generator component that generates acid upon exposure and a base component that exhibits a changed solubility in a developing solution under the action of acid.
Resins (base resins) are typically used as the base components for chemically amplified resist compositions.
For example, in an alkali developing process where an alkali developing solution is used as a developing solution, a chemically amplified resist composition for forming a positive resist pattern typically contains an acid generator component and a resin component that exhibits increased solubility in an alkali developing solution under the action of acid. If the resist film formed using the resist composition is selectively exposed during formation of a resist pattern, then within the exposed portions, acid is generated from the acid generator component, and the action of this acid causes an increase in the solubility of the resin component in an alkali developing solution, making the exposed portions soluble in the alkali developing solution. Therefore, a positive resist pattern in which the unexposed portions are remaining is formed by alkali developing.
As the resin component, a resin that exhibits increased polarity under the action of acid is typically used. When the polarity of the resin is increased, the solubility in an alkali developing solution increases whereas the solubility in an organic solvent is decreased. Therefore, when such a resin is applied to a solvent developing process using a developing solution containing an organic solvent (organic developing solution) instead of an alkali developing process, the solubility of the exposed portions in an organic developing solution is decreased. As a result, in the solvent developing process, the unexposed portions of the resist film are dissolved and removed by the organic developing solution, and a negative resist pattern in which the exposed portions are remaining is formed. This type of solvent developing process for forming a negative resist pattern is sometimes referred to as a “negative developing process” (for example, see Patent Document 1).
Currently, resins that contain structural units derived from (meth)acrylate esters within the main chain (acrylic resins) are now widely used as base resins for chemically amplified resist compositions that use ArF excimer laser lithography, as they exhibit excellent transparency in the vicinity of 193 nm (for example, see Patent Document 2). Here, the term “(meth)acrylate ester” is a generic term that includes either or both of the acrylate ester having a hydrogen atom bonded to the α-position and the methacrylate ester having a methyl group bonded to the α-position. The term “(meth)acrylate” is a generic term that includes either or both of the acrylate having a hydrogen atom bonded to the α-position and the methacrylate having a methyl group bonded to the α-position. The term “(meth)acrylic acid” is a generic term that includes either or both of acrylic acid having a hydrogen atom bonded to the α-position and methacrylic acid having a methyl group bonded to the α-position.
In general, the base resin contains a plurality of structural units for improving lithography properties and the like. For example, when the resin component is a resin that exhibits increased polarity under the action of acid, the resin typically contains a structural unit having an acid decomposable group which is decomposed by the action of an acid generated from the acid generator component to increase the polarity, as well as a structural unit having a polar group such as a hydroxyl group, a structural unit having a lactone structure, and the like. In particular, the structural units having a polar group are widely used, since the compatibility with an alkali developing solution is improved, which contributes to favorable improvements in the resolution.
In recent years, base resins containing a —SO2—NH— structure have been proposed (see, for example, Patent Documents 3 and 4). It is thought that these base resins exhibit excellent transparency in the vicinity of 193 nm wavelength and an adequate level of acidity, thereby contributing to the overall improvement of lithography properties in terms of high sensitivity, resolution and roughness.
As acid generators usable in a chemically amplified resist composition, various types have been proposed including, for example, onium salt-based acid generators; oxime sulfonate-based acid generators; diazomethane-based acid generators; nitrobenzylsulfonate-based acid generators; iminosulfonate-based acid generators; and disulfone-based acid generators. Of these, as an onium salt-based acid generator, iodonium salts containing an iodonium ion as the cation and sulfonium salts containing a sulfonium ion as the cation have been conventionally used. As an anion (acid) that forms a salt with these cations, a fluorinated alkylsulfonic acid ion is generally used (for example, see Patent Document 5). Further, as an anion, those having a —SO2—N—SO2 structure have been proposed (for example, see Patent Document 6).